This project is aimed at studying the molecular architecture of low resistance junctions (gap junctions) and the structural changes which modulate the junctional permeability. The goal for the current year was to learn the effects of Ca ions and Ca ions chelation on the structure of gap junctions isolated from mammalian liver. Preliminary results indicate that junctions isolated in the presence of EDTA are less resistant to detergent treatment allowing the isolation of apparently intact intramembrane particles. The free particles can be studied in detail after PTA negative staining and seem to be composed of either 12 subunits arranged in two parallel and interconnected rings of 6, or of 6 subunits with a dumbell shape, arranged in a circle with their long axis perpendicular to the plane of the circle. BIBLIOGRAPHIC REFERENCES: Peracchia, C., and M. E. Fernandez-Jaimovich. 1975. Isolation of intramembrane particles from gap junctions. J. Cell Biol. 67:330a.